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| 1 | Relaxation of Deformed Austenite and Refinement of Bainite in a Nb-Containing Microalloyed Steel显示文摘By means of stress relaxation and strain-induced precipitation in deformed austenite, bainite with micron sheaves size was ob-tained in Nb-containing steel. Microstructures of deformed samples isothermally relaxed for various time followed by cooling in water were examined. Stress relaxation test and transmission electron microscopy (TEM) were employed to detect precipitation of microalloy elements, such as Nb, Ti, during isothermal holding after deformation. All the samples were constituted by lath-like bainite along with acicular ferrite, but the size of bainitic sheaves and the amount of acicular ferrite were changed with relaxation time. To achieve optimum refinement, relaxation should be confined in the stage when the precipitates have sufficiently grown and started to coarsen. The sample having not undergone relaxation does not exhibit obvious refinement despite of its higher dislocation density. These results indicate that relaxation promotes bainite to refine, which is because deformed austenitic grains are divided by dislocation walls formed during rela-xation and acicular ferrite formed before bainitic transformation. | Shanwu Yang, Xuemin Wang, Chengjia Shang, Xinlai He, Yi Yuan Material Science and Engineering School, University of Science and Technology Beijing, Beijing 100083, China | 2001 | Journal of University of Science and Technology Beijing2001，8，3： | 24 |
| 2 | Microstructure and mechanical properties of Mg-Gd-Y-Sm-Al alloy and analysis of grain refinement and strengthening mechanism显示文摘The effects of Sm on the microstructure and mechanical properties of Mg-11 Gd-2 Y-0.6 Al alloy were investigated by X-ray diffraction,optical microscopy,scanning electron microscopy,energy dispersive spectrometry and high resolution transmission electron microscopy.Based on the theory of edge—edge matching and electronegativity theory,the mechanism of grain refinement is discussed.The strengthening mechanism is expounded conveniently from fine grain strengthening,coherent strengthening,precipitation strengthening and grain boundary strengthening.The results show that the micro structure of Mg-11 Gd-2 Y-0.6 Al alloy is mainly composed of a-Mg matrix,Mg5 Gd and Mg24Y5 phases.The addition of Sm forms Mg41Sm5 phase in the alloy and refines the alloy.The addition of Sm significantly improves the mechanical properties of the alloy at room and high temperatures.When the addition of Sm is 3 wt%,the tensile strengths of the alloy at room temperature and high temperature(200℃)reach the maximum value 292 and 321 MPa,respectively.The fracture mode of the alloy at different temperatures is mainly brittle fracture and intercrystalline fracture. | Xiaoya Chen Quanan Li Jun Chen Limin Zhu | 2019 | Journal of Rare Earths2019，37，12： | 12 |
| 3 | 界面捕捉Level Set方法的(AMR)数值模拟显示文摘在流体力学方程的计算中采用高精度WENO格式,用AMR(adaptive mesh refinement)方法提高流场局部分辨率,在采用Level Set函数标定物质界面的计算中用GFM(ghost fluid method)方法进行界面处理,尝试将AMR技术与界面追踪技术相互融合并应用于数值模拟,对不同的模拟结果进行了比较. | 宫翔飞 张树道 江松 | 2006 | 计算物理2006，23，4： | 11 |
| 4 | An adaptive version of ghost-cell immersed boundary method for incompressible flows with complex stationary and moving boundaries显示文摘An adaptive version of immersed boundary method for simulating flows with complex stationary and moving boundaries is presented.The method employs a ghost-cell methodology which allows for a sharp representation of the immersed boundary.To simplify the implementation of the methodology,a volume-of-fluid method is introduced to identify the immersed boundary.In addition,the domain is spatially discretized using a tree-based discretization which is relatively simple to implement a fully flexible adaptive refinement strategy.Finally,the methodology is validated by comparing it with numerical and experimental results on three cases:(1) the flow passing a circular cylinder at Re=40 and Re=100,(2) a periodic oscillation of a circular cylinder in fluid at rest and(3) the self-propelled fish-like swimming at Re=6400. | WANG Liang1 & WU ChuiJie2,3 1 School of Science,PLA University of Science and Technology,Nanjing 211101,China 2 State Key Laboratory of Structural Analysis for Industrial Equipment,Dalian University of Technology,Dalian 116024,China 3 School of Aeronautics and Astronautics,Dalian University of Technology,Dalian 116024,China | 2010 | Science China(Physics,Mechanics & Astronomy)2010，53，5： | 11 |
| 5 | Phase transformation refinement of coarse primary carbides in M2 high speed steel | Fu-sheng PAN Wei-qing WANG Ai-tao TANG Li-zhi WU Ting-ting LIU Ren-ju CHENG | 2011 | Progress in Natural Science:Materials International2011，21，2： | 10 |
| 6 | Effect of grain refinement on the hydrogen embrittlement of 304 austenitic stainless steel显示文摘The effect of grain size(in the range from 4 μm to 12 μm) on the hydrogen embrittlement(HE) of 304 austenitic stainless steel(ASS) was studied. HE susceptibility result shows that HE resistance increases with grain refinement. Electron backscattered diffraction kernel average misorientation(EBSD-KAM)mapping shows that the strain localization can be mitigated by grain refinement. Hence, strain localization sites which act as highways for hydrogen diffusion and preferred crack initiation sites can be reduced along with grain refinement, leading to a high HE resistance. Meanwhile, grain size shows no influence on the strain induced martensite(SIM) transformation during the hydrogen charging slow strain tensile test(SSRT). Hence, the SIM formed during hydrogen charging SSRT is not responsible for the different HE resistance of 304 ASSs with various grain sizes. Hydrogen diffusion is supposed to be controlled by a competition between short-circuit diffusion along random grain boundary(RGB) and hydrogen trapping at dislocations, leading to a maximum hydrogen diffusion coefficient in the 304 ASS with an average grain size of 8 μm. | Y.H.Fan B.Zhang J.Q.Wang E.-H.Han W.Ke | 2019 | Journal of Materials Science & Technology2019，35，10： | 10 |
| 7 | Effect of scanning speeds on electrochemical corrosion resistance of laser cladding TC4 alloy显示文摘In order to study the effect of scanning speed on the electrochemical corrosion resistance of laser cladding TC4 alloy in artificial seawater, the x-ray diffraction analysis, microstructure of cross-section, microhardness variation, and impedance spectrum have been studied in comparison with the TC4 titanium alloy. The results show that the main phase of cladding coating is α-Ti, and the change of scanning speed has no obvious effect on it; therefore, the supersaturated α-Ti solid solution is formed, and the acicular α martensite is obtained. As the scanning speed increases, the microstructure of cladding coating is orthogonal basket-weave, the crystal surface spacing decreases, and the average microhardness of laser cladding TC4 alloy slightly increases. When the scanning speed increases to 10 mm/s, the microhardness is about 14.71%higher than that of the substrate, and the electrochemical corrosion resistance of laser cladding TC4 alloy is also improved,which is about 2.48 times more than the substrate. Grain refinement has a great effect on enhancing the anti-electrochemical corrosion. | 冯晓甜 雷剑波 顾宏 周圣丰 | 2019 | Chinese Physics B2019，28，2： | 10 |
| 8 | Microstructure and mechanical properties of AZ91 magnesium alloy with minor additions of Sm, Si and Ca elements显示文摘The effects of Sm, Si and Ca on the microstructure and mechanical property of AZ91 magnesium alloy were investigated by means of optical microscopy (OM), differential scanning calorimetry (DSC), scanning electronic microscopy (SEM), X-ray diffraction (XRD) and tensile testing. The results indicated that the addition of 1.5 wt.% Sm with or without 0.8 Si/Ca led to a decrease in the volume fraction of the β-Mg17Al12 phase and the formation of the intermetallic compounds of Al-Sm, Mg2Si, MgAlCa and Al2Ca. The microstructure of AZ91 alloy was significantly refined and distribution became discrete with additions of Sm and Ca;the average grain size of the α-Mg matrix was reduced from 239.7 ± 16.9 μm to 66.34 ± 5.10 μm. The AZ91-Sm-Ca alloy exhibited a good combination of yield strength at 135 MPa, ultimate tensile strength at 199 MPa and elongation at 4.32%, which was ascribed to grain refinement strengthening. Furthermore, the T6 treated AZ91-Sm-Ca alloy possessed yield strength of 154 MPa and elongation of 7.1%, which was due to grain refinement strengthening and reduction in discontinuous precipitates. | Redeemina Comfort Bonnah Yu Fu Hai Hao | 2019 | China Foundry2019，16，5： | 9 |
| 9 | Microstructures and tensile properties of Mg-Zn-(Gd)-Zr alloys extruded at various temperatures显示文摘The microstructures and tensile properties of Mg-6.0 Zn-0.6 Zr(ZK60) and ZK60 + 1.8 Gd(ZEK620(RE = Gd)) alloys extruded at 290, 305, 320, 340 and360 ℃ were investigated. The results indicate that Gd addition can refine the microstructures of ZK60 alloy and the extrusion parameters such as the extrusion temperature will influence the tensile properties of both as-extruded ZK60 and ZEK620 alloys, although it is much slighter for ZK60 alloy. And the sensitivity is closely related to the textures developed during extrusion. In addition, Gd addition will also clearly improve the tensile strength at room temperature(24 ℃) and particularly at high temperatures(150 and 200 ℃), due to the much finer grains and smaller intermetallic particles. The highest strength is achieved in the as-extruded ZEK620 alloy with extrusion temperature of 320 ℃, with ultimate tensile strength(UTS) and tensile yield strength(TYS) of 405 and375 MPa, respectively, which are improved by approximately 9% and 11% than those of the as-extruded ZK60 alloy which owns the highest strength at extrusion temperature of 290 ℃. | Xin Qiu Qiang Yang Kai Guan Fanqiang Bu Zhan-Yi Cao Yong-Bing Liu Jian Meng | 2017 | Rare Metals2017，36，12： | 9 |
| 10 | An improved process for grain refinement of large 2219 Al alloy rings and its influence on mechanical properties显示文摘The large 2219 Al alloy rings used to connect propellant tank components of a satellite launch vehicle to each other are conventionally manufactured by radial-axial ring rolling at 460°C with 50% deformation,but often suffer from coarse elongated grain and low ductility. An improved process(hot ring rolling at460°C with 30% deformation, then air cooling to 240°C, followed by ring rolling at 240°C with 20% deformation) was tested for ring manufacturing. The corresponding microstructure evolution and mechanical properties of the produced rings were studied. The results show that the improved process can successfully be applied to manufacture the large 2219 Al alloy rings without formation of macroscopic defects,resulting in a product with fine and uniform grains after heat treatment. The fracture mechanism of both rings was mainly intergranular fracture. With the resulting grain size refinement due to the improved process, more homogeneous slip occured and the crack propagation path became more tortuous during the tensile testing process. Thus, the elongation in all three orthogonal directions was greatly improved,and the axial elongation increased from 3.5% to 10.0%. | Hailin He Youping Yi Shiquan Huang Yuxun Zhang | 2019 | Journal of Materials Science & Technology2019，35，1： | 9 |
| 11 | Towards better analysis of machine learning models:A visual analytics perspective显示文摘Interactive model analysis,the process of understanding,diagnosing,and refining a machine learning model with the help of interactive visualization,is very important for users to efficiently solve real-world artificial intelligence and data mining problems.Dramatic advances in big data analytics have led to a wide variety of interactive model analysis tasks.In this paper,we present a comprehensive analysis and interpretation of this rapidly developing area.Specifically,we classify the relevant work into three categories:understanding,diagnosis,and refinement.Each category is exemplified by recent influential work.Possible future research opportunities are also explored and discussed. | Shixia Liu Xiting Wang Mengchen Liu Jun Zhu | 2017 | Visual Informatics2017，1，1： | 9 |
| 12 | A two-step weighted least-squares method for joint estimation of source and sensor locations: A general framework显示文摘It is well known that the Two-step Weighted Least-Squares(TWLS) is a widely used method for source localization and sensor position refinement. For this reason, we propose a unified framework of the TWLS method for joint estimation of multiple disjoint sources and sensor locations in this paper. Unlike some existing works, the presented method is based on more general measurement model, and therefore it can be applied to many different localization scenarios.Besides, it does not have the initialization and local convergence problem. The closed-form expression for the covariance matrix of the proposed TWLS estimator is also derived by exploiting the first-order perturbation analysis. Moreover, the estimation accuracy of the TWLS method is shown analytically to achieve the Cramér-Rao Bound(CRB) before the threshold effect takes place. The theoretical analysis is also performed in a common mathematical framework, rather than aiming at some specific signal metrics. Finally, two numerical experiments are performed to support the theoretical development in this paper. | Ding WANG Jiexin YIN Tao TANG Ruirui LIU Zhidong WU | 2019 | Chinese Journal of Aeronautics2019，32，2： | 8 |
| 13 | Effect of Ce on the cleanliness, microstructure and mechanical properties of high strength low alloy steel Q690E in industrial production process显示文摘In order to improve the strength and toughness of Q690 E steel sheets,the effect of rare earth element Ce on the strength and toughness of Q690 E steel was studied by means of transmission electron microscopy,scanning electron microscopy,and metallographic microscope.The results showed that the addition of Ce in steel limited the combination of S with Mn and Ca,transformed Al2O3 inclusion into spherical CeAlO3 inclusion,and modified the precipitate form of some composite inclusions of TiN and sulfide oxides into TiN precipitation alone.The inclusions were spheroidizing.The size of inclusions was decreased from 3–5μm to 1–2μm,and the distribution was dispersed.Ce played a role in purifying molten steel through desulphurization and deoxidization.Meanwhile,the addition of Ce in steel effectively increased the nucleation particles in the liquid phase,improved the nucleation rate,enlarged the equiaxed grain refinement area,and limited the development of columnar crystals.The average grain size of slab decreased from 45.76 to 35.25μm,and the proportion of large grain size(>50μm)decreased from 40.41%to 23.74%.The macrostructural examination of slab was improved from B0.5 to C2.0,which realized the refinement of the solidified structure and reduced the banded structure of hot rolled plate.In addition,due to the inheritance of refined structure in the upstream,the recrystallization of deformed austenite and the growth of grain after recrystallization were restrained,and a refined tempered sorbite structure was obtained.When rare earth element Ce was added,the width of the martensite lath bundle was narrowed from about 500 nm to about 200 nm,which realized a remarkable grain refinement strengthening and toughening effect.Mechanical properties such as tensile,yield,and low-temperature impact toughness were significantly improved. | Hao Wang Yan-ping Bao Ming Zhao Min Wang Xiao-ming Yuan Shuai Gao | 2019 | International Journal of Minerals,Metallurgy and Materials2019，26，11： | 7 |
| 14 | Effect of the simultaneous application of a high static magnetic field and a low alternating current on grain structure and grain boundary of pure aluminum显示文摘Effect of the simultaneous application of a high static magnetic field and a low alternating electric current on the solidification structure of pure aluminum has been investigated. Results show that the refinement of the solidification structure is enhanced by the electric current under a certain magnetic field. However,when the magnetic field intensity exceeds a certain value, the refinement is impaired under a certain electric current. The observation by electron backscattered diffraction(EBSD) shows the complex fields have led to the increase of the low angle boundaries with the refinement. Moreover, the application of the static gradient magnetic field is capable of modifying the distribution of the refined grains. The above results may be attributed to the formation of the cavities during the electromagnetic vibration process and the high magnetic field. | Chengshuai Li Shaodong Hu Zhongming Ren Yves Fautrelle Xi Li | 2018 | Journal of Materials Science & Technology2018，34，12： | 7 |
| 15 | DEFORMATION ENHANCED FERRITE TRANSFORMATION IN PLAIN LOW CARBON STEEL显示文摘The microstructure evolution during deformation enhanced transformation of under cooled austenite of a plain low carbon steel has been investigated by means of hot compression simulation experiment under various conditions of strain rate,deforma- tion temperature and strain. The effect of austenite grain size on the strain enhanced ferrite transformation has been studied. The ferrite dynamic recrystallization involved in successive hot deformation has been explored. | Z.Q. Sun, W Y. Yang, A.M. Hu and P. Yang (State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China) (School of Material Science and Engineering, University of Science and Technology Beijin | 2001 | Acta Metallurgica Sinica(English Letters)2001，14，2： | 7 |
| 16 | Microstructure refinement and work hardening in a machined surface layer induced by turning Inconel 718 super alloy显示文摘The microstructural changes in the machined surface layer of Ni-based super alloys essentially determine the final performance of the structural components of aerospace engines in which these alloys are used.In this work,multiscale metallurgical observations using scanning electron microscopy,electron-backscatter diffraction microscopy,and transmission electron microscopy were conducted to quantitatively characterize the microstructure of the machined subsurface.Next,to elucidate the factors that affect the formation of the refinement microstructure,the distributions of the deformation parameters(strain,strain rate,and temperature) in the machined subsurface were analyzed.A dislocation–twin interaction dynamic recrystallization mechanism for grain refinement during machining of Inconel 718 is proposed.Furthermore,microhardness evolution induced by grain refinement in the machined surface is evaluated.The results suggest that the gradient microstructure and the work hardening can be optimized by controlling the cutting parameters during turning of Inconel 718. | Xiao-ping Ren Zhan-qiang Liu | 2018 | International Journal of Minerals,Metallurgy and Materials2018，25，8： | 7 |
| 17 | Finite element analyses of slope stability problems using non-associated plasticity显示文摘In recent years, finite element analyses have increasingly been utilized for slope stability problems. In comparison to limit equilibrium methods, numerical analyses do not require any definition of the failure mechanism a priori and enable the determination of the safety level more accurately. The paper compares the performances of strength reduction finite element analysis(SRFEA) with finite element limit analysis(FELA), whereby the focus is related to non-associated plasticity. Displacement-based finite element analyses using a strength reduction technique suffer from numerical instabilities when using non-associated plasticity, especially when dealing with high friction angles but moderate dilatancy angles. The FELA on the other hand provides rigorous upper and lower bounds of the factor of safety(FoS) but is restricted to associated flow rules. Suggestions to overcome this problem, proposed by Davis(1968), lead to conservative FoSs; therefore, an enhanced procedure has been investigated. When using the modified approach, both the SRFEA and the FELA provide very similar results. Further studies highlight the advantages of using an adaptive mesh refinement to determine FoSs. Additionally, it is shown that the initial stress field does not affect the FoS when using a Mohr-Coulomb failure criterion. | Simon Oberhollenzer Franz Tschuchnigg Helmut F.Schweiger | 2018 | Journal of Rock Mechanics and Geotechnical Engineering2018，10，6： | 6 |
| 18 | Surface grain refinement mechanism of SMA490BW steel cross joints by ultrasonic impact treatment显示文摘Ultrasonic impact treatment(UIT) is a postweld technique for improving the fatigue strength of welded joints. This technique makes use of ultrasonic vibration to impact and plastically deform a weld toe and can achieve surface grain refinement of the weld toe,which is considered as the main reason for the improvement of fatigue strength. In this paper,the microstructure of the surface of a treated weld toe was observed by metallographic microscopy and transmission electron microscopy(TEM). The results show that UIT could produce severe plastic deformation on the surface layer of the weld toe and the maximum depth of plastic deformation extended to approximately 260 μm beneath the treated surface. Repeated processing could exacerbate the plastic deformation on the surface layer,resulting in finer grains. We can conclude that the surface grain refinement mechanism of SMA490 BW welded joints is related to the high density of dislocation tangles and dislocation walls. | Bo-lin He Lei Xiong Ming-ming Jiang Ying-xia Yu Li Li | 2017 | International Journal of Minerals,Metallurgy and Materials2017，24，4： | 6 |
| 19 | Microstructural evolution of aluminum alloy during friction stir welding under different tool rotation rates and cooling conditions显示文摘The microstructural evolution during friction stir welding(FSW) has long been studied only using one single welding parameter. Conclusions were usually made based on the final microstructure observation and hence were one-sided. In this study, we used the 'take-action' technique to freeze the microstructure of an Al-Mg-Si alloy during FSW, and then systematically investigated the microstructures along the material flow path under different tool rotation rates and cooling conditions. A universal characteristic of the microstructural evolution including four stages was identified, i.e. dynamic recovery(DRV), dislocation multiplication, new grain formation and grain growth. However, the dynamic recrystallization(DRX)mechanisms in FSW depended on the welding condition. For the air cooling condition, the DRX mechanisms were related to continuous DRX associated with subgrain rotation and geometric DRX at high and low rotation rates, respectively. Under the water cooling condition, we found a new DRX mechanism associated with the progressive lattice rotation resulting from the pinning of the second-phase particles.Based on the analyses of the influencing factors of grain refinement, it was clearly demonstrated that the delay of DRV and DRX was the efficient method to refine the grains during FSW. Besides, ultra-high strain rate and a short duration at high temperatures were the key factors to produce an ultrafine-grained material. | X.H. Zeng P. Xue L.H. Wu D.R. Ni B.L. Xiao K.S. Wang Z.Y. Ma | 2019 | Journal of Materials Science & Technology2019，35，6： | 6 |
| 20 | Evolution of secondary phase particles during deformation of Al-5Ti-1B master alloy and their effect on α-Al grain refinement显示文摘Addition of Al-5Ti-1B alloy to molten aluminum alloys can refine α-Al grains effectively and thereby improve their strength and toughness. TiAl_3 and TiB_2 in Al-5Ti-1B alloy are the main secondary-phase particles for refinement, while the understanding on the effect of their sizes on α-Al grain refinement continues to be fragmented. Therefore, Al-5Ti-1B alloys with various sizes and morphologies of the secondary-phase particles were prepared by equal channel angular pressing(ECAP). Evolution of the secondary-phase particles during ECAP process and their impact on α-Al grain refinement were studied by X-ray diffraction and scanning electron microscope(SEM). Results show that during the ECAP process, micro-cracks firstly appeared inside TiAl_3 particles and then gradually expanded, which resulted in continuous refinement of TiAl_3 particles. In addition, micro-distribution uniformity of TiB_2 particles was improved due to the impingement of TiAl_3 particles to TiB_2 clusters during deformation. Excessively large sizes of TiAl_3 particles would reduce the number of effective heterogeneous nucleus and thus resulted in poor grain refinement effectiveness. Moreover, excessively small TiAl_3 particles would reduce inhibitory factors for grain growth Q and weaken grain refinement effectiveness. Therefore, an optimal size range of 18-22 μm for TiAl_3 particles was suggested. | Hong Yu Ning Wang Renguo Guan Di Tie Zheng Li Yanan An Yang Zhang | 2018 | Journal of Materials Science & Technology2018，34，12： | 6 |
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